THE RAS-LIKE RAB3A PROTEIN IS PRESENT IN PINEALOCYTES OF THE GERBIL PINEAL-GLAND

As part of our molecular and functional characterization of the compar tment of synaptic-like microvesicles (SLMVs) in mammalian pinealocytes , we have now analyzed the pineal gland of the Mongolian gerbil for th e presence of rab3 proteins. Members of this subfamily of small G prot eins are thought to regulate the intracellular trafficking and/or memb rane fusion of secretory vesicles. Immunostaining of serial semi-thin sections of plastic-embedded pineals with monoclonal antibodies which recognize rab3A revealed the occurrence of rab3A in pinealocytes throu ghout the gland. Rab3A immunoreactivity was markedly enriched in dilat ed pinealocyte process terminals known to contain accumulations of SLM Vs. The latter could be labeled with the rab3 antibodies at the ultras tructural level when immunogold staining was performed. Our results le nd further support to the hypothesis that mammalian pinealocytes are e ndowed with a population of SLMVs that serve secretory functions.